BackgroundRotavirus is the most common cause of severe gastroenteritis among children. We conducted hospital-based surveillance to estimate the burden of hospitalizations for rotavirus among children aged <5 years and to describe strain distribution patterns during the 2-year study period MethodsChildren aged <5 years with diarrhea were prospectively enrolled and evaluated by trained pediatricians at representative hospitals in Mongolia and Sri Lanka. Fecal specimens were tested by rotavirus antigen detection enzyme immunoassay. Specimens that tested positive for rotavirus were further characterized to determine the genotype of strains by reverse-transcriptase polymerase chain reaction ResultsFrom 1 March 2005 through 28 February 2007, a total of 1277 hospitalized children with diarrhea were enrolled in Mongolia, and 1916 were enrolled in Sri Lanka. Of the 1152 children in Mongolia who had samples tested, 458 (40%) had results positive for rotavirus, and in Sri Lanka, 428 (24%) of 1806 children with samples tested had positive results. G3P8 was the most common genotype among rotavirus strains in Mongolia (68%) and Sri Lanka (15%) ConclusionsRotavirus causes 40% and 24% of hospitalizations for diarrhea among children in Mongolia and Sri Lanka, respectively. Each study site will continue surveillance of rotavirus, and additional laboratory testing will be performed to provide additional information on the distribution of rotavirus strains by G and P genotype